Shovel and method of controlling shovel

ABSTRACT

A shovel includes a turning electric motor configured to drive a turning body to turn and a turning brake hydraulic motor mechanically connected to the turning body or the turning electric motor. In a state where a turning operation part for turning the turning body is unoperated, the turning body is braked using the turning brake hydraulic motor and the braking operation of a mechanical brake unit for mechanically holding the turning body stationary is released when an operation part for performing an operation other than the turning of the turning body is operated.

TECHNICAL FIELD

The present invention relates to shovels that use an electric motor toelectrically drive a turning body.

BACKGROUND ART

In general, shovels that perform excavation or the like are providedwith a turning body, and the turning body is provided with a boom, anarm, and a bucket for performing excavation. By causing the turning bodyto turn, the bucket is moved to a position around the shovel. Causingthe turning body to turn with a turning hydraulic motor is referred toas hydraulic turning. Furthermore, causing the turning body to turn witha turning electric motor is referred to as electric turning.

In shovels that adopt electric turning, a turning electric motor isfreely rotatable and is therefore mechanically braked and heldstationary when the turning electric motor is not driven. A brake unit,which applies mechanical braking, keeps the turning body stationaryusing a frictional force. As a consequence, the brake unit has a problemin that a component that generates a frictional force is subject towear. When the shovel is in operation, a large external force acts onthe turning body. Therefore, the braking force (frictional force) has tobe maintained against this large external force. As a consequence, aload applied on the brake unit is so large that part of the brake unitthat generates a frictional force is worn out in a short time, thuscausing the problem of a short service life of the brake unit.

Therefore, it has been proposed to keep the turning body stationary bysubjecting a turning electric motor to zero speed control (see, forexample, Patent Document 1). The zero speed control is control thatkeeps a turning electric motor constantly driven and maintains therotational speed at zero by driving the turning electric motor in areverse direction so that the rotational speed becomes zero, when theturning electric motor is caused to rotate by an external force.Maintaining the rotational speed of the turning electric motor at zerois to prevent the turning electric motor from rotating. Accordingly, theturning body is kept at a fixed position.

PRIOR ART DOCUMENT Patent Document

[Patent Document 1] Japanese Laid-Open Patent Application No.2005-299102

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

According to control that keeps a turning body stationary by subjectinga turning electric motor to zero speed control, the turning electricmotor is driven to generate such a turning force as to cancel out anexternal force applied to the turning body. Therefore, the turningelectric motor has to be constantly driven, so that it is necessary tosupply electric power to the turning electric motor in order to hold theturning body stationary. Accordingly, a large amount of electric powerhas to be supplied from an electric energy storage unit to the turningelectric motor, so that the state of charge of the electric energystorage device may suddenly lower. Furthermore, this is not preferablein terms of power saving, either, because the turning electric motorconsumes electric power not for performing operations but just forbraking.

The present invention is made in view of the above-described problems,and has an object of providing a shovel that is capable of keeping aturning body stationary using a brake unit other than mechanical brakesand does not require a large amount of electric power to generate abraking force.

Means for Solving the Problems

According to the present invention, a shovel is provided that ischaracterized by including a turning electric motor configured to drivea turning body to turn and a turning brake hydraulic motor mechanicallyconnected to the turning body or the turning electric motor.

Preferably, the above-described shovel further includes a hydrauliccircuit configured to disconnect the intake port and the discharge portof the turning brake hydraulic motor. In a state where a turningoperation part for turning the turning body is unoperated, the turningbody may be braked using the turning brake hydraulic motor when anoperation part for performing an operation other than turning isoperated. Furthermore, in the state where the turning operation part forturning the turning body is unoperated, the braking operation of amechanical brake unit for mechanically holding the turning bodystationary may be released when the operation part for performing theoperation other than turning is operated.

Furthermore, the hydraulic circuit may be configured to keep a dischargeside of the turning brake hydraulic motor closed, and a connecting anddisconnecting device may be provided between the turning body and theturning brake hydraulic motor. The connecting and disconnecting devicemay be configured to connect the turning brake hydraulic motor to theturning body or the turning electric motor in a state where a turningoperation part for turning the turning body is unoperated. Furthermore,the hydraulic circuit may include a switching valve and may beconfigured to disconnect the intake port and the discharge port of theturning brake hydraulic motor by the switching valve. Furthermore, whena turning operation part for turning the turning body is operated, theintake port and the discharge port of the turning brake hydraulic motormay be connected by the switching valve to form a closed circuit, andwhen the turning operation part for turning the turning body isunoperated, the intake port and the discharge port of the turning brakehydraulic motor may be disconnected by the switching valve.

Effects of the Invention

According to the above-described invention, it is possible to keep aturning body stationary using a brake unit other than mechanical brakesand to prevent a large amount of electric power from being consumed togenerate a braking force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a hybrid shovel.

FIG. 2 is a block diagram illustrating a configuration of a drive systemof a hybrid shovel according to a first embodiment.

FIG. 3 is a block diagram illustrating a configuration of an electricenergy storage system.

FIG. 4 is a block diagram illustrating a configuration of a turningdrive system that includes a turning brake hydraulic motor for causing ahydraulic braking force to be generated.

FIG. 5 is a flowchart of a control process in the case of performingoperations with the turning of an upper-part turning body being stopped.

FIG. 6 is a block diagram illustrating a configuration of a turningdrive system that includes a turning brake hydraulic motor according toa second embodiment of the present invention.

FIG. 7 is a block diagram illustrating a configuration of a drive systemof a series hybrid shovel.

FIG. 8 is a block diagram illustrating a configuration of a drive systemof an electric shovel.

DESCRIPTION OF EMBODIMENTS

A description is given, with reference to the drawings, of embodimentsof the present invention.

FIG. 1 is a side view illustrating a hybrid shovel to which the presentinvention is applied.

An upper-part turning body 3 is mounted through a turning mechanism 2 ona lower-part traveling body 1 of the hybrid shovel. A boom 4 is attachedto the upper-part turning body 3. An arm 5 is attached to the end of theboom 4. A bucket 6 is attached to the end of the arm 5. The boom 4, thearm 5, and the bucket 6 are hydraulically driven by a boom cylinder 7,an arm cylinder 8, and a bucket cylinder 9, respectively. A cabin 10 andpower sources such as an engine are mounted on the upper-part turningbody 3.

Shovels to which the present invention may be applied are not limited tohybrid shovels. The present invention may also be applied to any shovelsthat adopt electric turning, such as electrically driven shovels thatare supplied with charging electric power from an external power source.

FIG. 2 is a block diagram illustrating a configuration of a drive systemof the hybrid shovel according to the first embodiment. In FIG. 2, amechanical power system, a high-pressure hydraulic line, a pilot line,and an electric drive and control system are indicated by a double line,a solid line, a broken line, and a solid line, respectively.

An engine 11 as a mechanical drive part and a motor generator 12 as anassist drive part are connected to a first input shaft and a secondinput shaft, respectively, of a transmission 13. A main pump 14 and apilot pump 15 are connected as hydraulic pumps to the output shaft ofthe transmission 13. A control valve 17 is connected to the main pump 14via a high-pressure hydraulic line 16.

The control valve 17 is a controller configured to control a hydraulicsystem in the hybrid shovel. Hydraulic motors 1A (right) and 1B (left)for the lower-part traveling body 1, the boom cylinder 7, the armcylinder 8, and the bucket cylinder 9 are connected to the control valve17 via high-pressure hydraulic lines.

An electric energy storage system (electric energy storage unit) 120including a capacitor as an electric energy storage device is connectedto the motor generator 12 via an inverter 18A. A turning electric motor21 as an electric working element is connected to the electric energystorage system 120 via an inverter 20. A resolver 22, a mechanical brake23, and a turning transmission 24 are connected to a rotation shaft 21Aof the turning electric motor 21. Furthermore, an operation apparatus 26is connected to the pilot pump 15 via a pilot line 25. The turningelectric motor 21, the inverter 20, the resolver 22, the mechanicalbrake 23, and the turning transmission 24 constitute a load drivesystem. Here, the turning electric motor 21 corresponds to a turningelectric motor for turning the upper-part turning body 3, and themechanical brake 23 corresponds to a brake unit that mechanically brakesthe upper-part turning body 3.

The operation apparatus 26 includes a lever 26A, a lever 26B, and apedal 26C. The lever 26A, the lever 26B, and the pedal 26C are connectedto the control valve 17 and a pressure sensor 29 via hydraulic lines 27and 28, respectively. The pressure sensor 29 is connected to acontroller 30 that controls the driving of the electric system of thehybrid shovel.

FIG. 3 is a block diagram illustrating the electric energy storagesystem 120. The electric energy storage system 120 includes a capacitor19 as an electric energy storage device, a step-up/step-down converter100, and a DC bus 110. The DC bus 110 as a second electric energystorage device controls the transfer of electric power among thecapacitor 19 as a first electric energy storage device, the motorgenerator 12, and the turning electric motor 21. The capacitor 19 isprovided with a capacitor voltage detecting part 112 for detecting acapacitor voltage value and a capacitor electric current detecting part113 for detecting a capacitor electric current value. The capacitorvoltage value and the capacitor electric current value detected by thecapacitor voltage detecting part 112 and the capacitor electric currentdetecting part 113, respectively, are fed to the controller 30.

The step-up/step-down converter 100 performs such control as switching astep-up operation and a step-down operation in accordance with theoperating states of the motor generator 12 and the turning electricmotor 21, so that the DC bus voltage value falls within a certain range.The DC bus 110 is provided between the inverters 18A and 20 and thestep-up/step-down converter 100 to transfer electric power among thecapacitor 19, the motor generator 12, and the turning electric motor 21.

Referring back to FIG. 2, the controller 30 is a control unit serving asa main control part that controls the driving of the hybrid shovel. Thecontroller 30 includes a processor including a CPU (Central ProcessingUnit) and an internal memory. The controller 30 is implemented by theCPU executing a drive control program contained in the internal memory.

The controller 30 converts a signal fed from the pressure sensor 29 intoa speed command, and controls the driving of the turning electric motor21. The signal fed from the pressure sensor 29 corresponds to a signalrepresenting the amount of operation in the case of operating theoperation apparatus 26 to turn the turning mechanism 2.

The controller 30 controls the operation (switches the electric motor[assist] operation and the generator operation) of the motor generator12. The controller 30 also controls the charge and discharge of thecapacitor 19 by controlling the driving of the step-up/step-downconverter 100 as a step-up/step-down control part. The controller 30controls the charge and discharge of the capacitor 19 by controlling theswitching of the step-up operation and the step-down operation of thestep-up/step-down converter 100 based on the state of charge of thecapacitor 19, the operating state (electric motor [assist] operation orgenerator operation) of the motor generator 12, and the operating state(power running operation or regenerative operation) of the turningelectric motor 21. The controller 30 also controls the amount ofcharging (charging electric current or charging electric power) of thecapacitor 19 as described below.

This control of the switching of the step-up operation and the step-downoperation of the step-up/step-down converter 100 is performed based onthe DC bus voltage value detected by a DC bus voltage detecting part111, the capacitor voltage value detected by the capacitor voltagedetecting part 112, and the capacitor electric current value detected bythe capacitor electric current detecting part 113.

In the above-described configuration, the electric power generated bythe motor generator 12, which is an assist motor, is supplied to the DCbus 110 of the electric energy storage system 120 via the inverter 18Ato be supplied to the capacitor 19 via the step-up/step-down converter100. The electric power regenerated by the regenerative operation of theturning electric motor 21 is supplied to the DC bus 110 of the electricenergy storage system 120 via the inverter 20, to be supplied to thecapacitor 19 via the step-up/step-down converter 100.

The rotational speed (angular velocity ω) of the turning electric motor21 is detected by the resolver 22. Furthermore, the angle of the boom 4(boom angle θB) is detected by a boom angle sensor 7B such as a rotaryencoder provided on the support shaft of the boom 4. The controller 30determines an estimated turning regenerated electric power (energy) byoperations based on the angular velocity o of the turning electric motor21, and determines an estimated boom regenerated electric power (energy)by operations based on the boom angle θB. Then, the controller 30determines the anticipated regeneration target value of the SOC byoperations based on the estimated turning regenerated electric power andestimated boom regenerated electric power determined by operations. Thecontroller 30 controls the parts of the hybrid shovel so that the SOC ofthe capacitor 19 approaches the determined anticipated regenerationtarget value.

The hybrid shovel of the above-described configuration may performoperations such as excavation by driving the boom 4, the arm 5, and thebucket 6 while holding the upper-part turning body 3 at a fixed turningposition. In this case, the upper-part turning body 3 is braked by themechanical brake 23 so as not to be caused to turn by an external force.The mechanical brake 23 is automatically caused to operate in responseto the absence of operation of a turning operation lever (for example,the lever 26A) of the operation apparatus 26 for a certain period oftime. The mechanical brake 23 is released immediately in response to theoperation of the turning operation lever.

This embodiment prevents the occurrence of a state where an operationusing the boom 4, the arm 5, or the bucket 6 is performed with theapplication of the mechanical brake 23. That is, at the time ofperforming operations with the upper-part turning body 3 beingstationary, the mechanical brake 23 is released and a braking force isgenerated using a hydraulic pressure instead to brake the upper-partturning body 3 into a stationary state. According to this embodiment,for example, a hydraulic pump is used as a hydraulic apparatus forcausing a hydraulic braking force to be generated.

FIG. 4 is a block diagram illustrating a configuration of a turningdrive system including a turning brake hydraulic motor for causing ahydraulic braking force to be generated. In FIG. 4, the same componentsas the components illustrated in FIG. 2 are given the same symbols andtheir description is omitted.

In this embodiment, the drive shaft of a turning brake hydraulic motor40 is mechanically connected to the output shaft of the turning electricmotor 21. The turning brake hydraulic motor 40 is a hydraulic pumpincluding a port 40 a and a port 40 b. When the drive shaft of theturning brake hydraulic motor 40 is caused to rotate in one direction,the port 40 a serves as an intake port and the port 40 b serves as adischarge port so as to cause hydraulic fluid to flow from the port 40 ato the direction of the port 40 b. When the drive shaft of the turningbrake hydraulic motor 40 is caused to rotate in the opposite direction,the port 40 b serves as an intake port and the port 40 a serves as adischarge port so as to cause hydraulic fluid to flow from the port 40 bto the direction of the port 40 a.

Here, closing the port 40 a and the port 40 b to prevent hydraulic fluidfrom flowing prevents the drive shaft of the turning brake hydraulicmotor 40 from rotating. The drive shaft of the turning brake hydraulicmotor 40 is mechanically connected to the output shaft of the turningelectric motor 21. Therefore, when the drive shaft of the turning brakehydraulic motor 40 is prevented from rotating, the output shaft of theturning electric motor 21 as well is prevented from rotating, so thatthe upper-part turning body 3 as well is prevented from turning.Accordingly, by preventing hydraulic fluid from flowing by closing theport 40 a and the port 40 b of the turning brake hydraulic motor 40, theupper-part turning body 3 is braked, so that it is possible to keep theupper-part turning body 3 stationary.

A hydraulic circuit 50 is connected to the turning brake hydraulic motor40, so that the flow of hydraulic fluid is controlled by the hydrauliccircuit 50. The hydraulic circuit 50 includes a switching valve 60. Theswitching valve 60 performs switching to either a state where a fluidpassage 50 a connected to the port 40 a of the turning brake hydraulicmotor 40 and a fluid passage 50 b connected to the port 40 b of theturning brake hydraulic motor 40 are connected or a state where thefluid passage 50 a and the fluid passage 50 b are disconnected. Theoperation of the switching valve 60 is controlled by a switching signalfrom the controller 30. FIG. 4 illustrates a state where the fluidpassage 50 a and the fluid passage 50 b are disconnected by theswitching valve 60. Disconnecting the fluid passage 50 a and the fluidpassage 50 b corresponds to closing the port 40 a and the port 40 b ofthe turning brake hydraulic motor 40.

Accordingly, by disconnecting the fluid passage 50 a and the fluidpassage 50 b using the switching valve 60, it is possible to brake andkeep stationary the upper-part turning body 3.

On the other hand, when the fluid passage 50 a and the fluid passage 50b are connected by the switching valve 60, hydraulic fluid that flowsfrom the fluid passage 50 a to the port 40 a of the turning brakehydraulic motor 40 is taken in into the turning brake hydraulic motor 40to be discharged from the port 40 b. The hydraulic fluid discharged fromthe port 40 b flows through the fluid passage 50 b to return again tothe switching valve 60, and flows through the fluid passage 50 a to betaken in into the port 40 a of the turning brake hydraulic motor 40.Thus, by forming a closed circuit by connecting the fluid passage 50 aand the fluid passage 50 b using the switching valve 60, it is possibleto drive the turning brake hydraulic motor 40 in an idling state. Inthis state, braking by the turning brake hydraulic motor 40 is released,so that the upper-part turning body 3 may be driven to turn. That is, atthe time of turning the upper-part turning body 3, the fluid passage 50a and the fluid passage 50 b are connected by operating the switchingvalve 60.

The hydraulic circuit 50 includes relief valves 52A and 52B and checkvalves 54A and 54B. The relief valves 52A and 52B and the check valves54A and 54B are provided to release a hydraulic pressure in order toprevent hydraulic pressures inside the fluid passage 50 a and the fluidpassage 50 b from becoming excessively high. For example, when anexternal force (turning force) acting on the upper-part turning body 3becomes so large that the hydraulic pressure inside the fluid passage 50b excessively increases to exceed the relief pressure of the reliefvalve 52B, high-pressure hydraulic fluid flows out from the relief valve52B to the fluid passage 50 a through the check valve 54A. As a result,the hydraulic pressure inside the fluid passage 50 b decreases to bemaintained at or below the relief pressure of the relief valve 52B. Thehydraulic pressure inside the fluid passage 50 a is maintained at orbelow the relief pressure of the relief valve 52A in the same mannerwhen the hydraulic pressure inside the fluid passage 50 a excessivelyincreases.

Therefore, it is possible to prevent damage to the components of theturning drive system.

Next, a description is given of control in the case of performingoperations with the turning of the upper-part turning body 3 beingstopped. FIG. 5 is a flowchart of a control process in the case ofperforming operations with the turning of the upper-part turning body 3being stopped.

First, at step S1, it is determined whether all operation levers(operation parts) are unoperated. If it is determined that all operationlevers (operation parts) are not unoperated (NO at step S1), the processproceeds to step S4. On the other hand, if it is determined that alloperation levers (operation parts) are unoperated (YES at step S1), theprocess proceeds to step S2, where it is determined whether apredetermined time (for example, five seconds) has passed. During anoperation such as excavation or ground leveling, the process proceedsfrom step S1 to step S4.

If it is determined at step S2 that a predetermined time (for example,five seconds) has not passed, the process returns to step S1. On theother hand, if it is determined at step S2 that a predetermined time(for example, five seconds) has passed, the process proceeds to step S3,where the mechanical brake 23 (a parking brake) is turned ON. That is,when an operation lever for turning the upper-part turning body 3 is notoperated for a predetermined time (for example, five seconds), it isdetermined that the upper-part turning body 3 is to be held stationary,and the mechanical brake 23 is caused to operate to apply braking, so asto hold the upper-part turning body 3 in its position.

Next, at step S4, it is determined whether an operation lever other thanthe operation lever for turning the upper-part turning body 3 has beenoperated. If an operation lever other than the operation lever forturning the upper-part turning body 3 has not been operated (NO at stepS4), the process of this time ends. The absence of operation of anoperation lever other than the operation lever for turning theupper-part turning body 3 means that no other working elements areoperated while the upper-part turning body 3 is stationary, either, sothat it may be determined that the shovel is doing no operation.Accordingly, the state is maintained where braking is applied by themechanical brake 23.

On the other hand, if an operation lever other than the operation leverfor turning the upper-part turning body 3 has been operated (YES at stepS4), the process proceeds to step S5, the switching valve 6 is caused tooperate so that the fluid passage 50 a and the fluid passage 50 b aredisconnected (the state illustrated in FIG. 4). That is, when anoperation other than the turning of the upper-part turning body 3 hasbeen performed while the upper-part turning body 3 is stationary, it isdetermined that an operation with the bucket 6 or the like is beingperformed with the upper-part turning body 3 being stationary, and thedrive shaft of the turning brake hydraulic motor 40 is prevented fromrotating to brake the upper-part turning body 3. The flow of hydraulicfluid is blocked by disconnecting the fluid passage 50 a and the fluidpassage 50 b, so that the drive shaft of the turning brake hydraulicmotor 40 is prevented from rotating. Therefore, the turning electricmotor 21 is prevented from rotating, so that the upper-part turning body3 as well is prevented from turning.

After the application of braking by the turning brake hydraulic motor40, the operation of the mechanical brake (parking brake) 23 is releasedat step S6. That is, because braking has been applied by the turningbrake hydraulic motor 40, it is possible to keep the upper-part turningbody 3 stationary even when the braking applied by the mechanical brake23 is released. Therefore, the wear of friction parts (for example, abrake lining) of the mechanical brake 23 is prevented, so that it ispossible to prevent friction parts of the mechanical brake 23 from beingworn early. As a result, it is possible to extend the service life ofthe mechanical brake 23. Then, after the release of the mechanical brakeat step S6, the process is restarted from step S1.

Next, a description is given of a second embodiment. FIG. 6 is a blockdiagram illustrating a configuration of a turning drive system includinga turning brake hydraulic motor according to the second embodiment ofthe present invention. In FIG. 6, the same components as the componentsillustrated in FIG. 4 are given the same symbols, and their descriptionis omitted.

As illustrated in FIG. 6, according to this embodiment, the hydrauliccircuit 50 does not include the switching valve 60. Accordingly, in thehydraulic circuit 50 illustrated in FIG. 7, the port 40 a and the port40 b of the turning brake hydraulic motor 40 are prevented fromdischarging hydraulic fluid and are kept closed. That is, the turningbrake hydraulic motor 40 is kept braked. If the turning brake hydraulicmotor 40 remains as it is, the upper-part turning body 3 is preventedfrom being driven to turn. Therefore, according to this embodiment, inplace of the switching valve 60, a connecting and disconnecting device70 is provided between the turning brake hydraulic motor 40 and theturning electric motor 21.

Like, for example, a clutch, the connecting and disconnecting device 70allows the transmission of a turning force by engaging two members witheach other and prevents the transmission of a turning force bydisengaging the two members. That is, the connecting and disconnectingdevice 70 may connect and disconnect the drive shaft of the turningbrake hydraulic motor 40 and the output shaft of the turning electricmotor 21 based on a signal from the controller 30. Accordingly, whenbraking is applied with the turning brake hydraulic motor 40, the driveshaft of the turning brake hydraulic motor 40 and the output shaft ofthe turning electric motor 21 are connected by the connecting anddisconnecting device 70. On the other hand, when the upper-part turningbody 3 is driven to turn by driving the turning electric motor 21, thedrive shaft of the turning brake hydraulic motor 40 and the output shaftof the turning electric motor 21 are disconnected by the connecting anddisconnecting device 70.

Thus, according to this embodiment, the turning brake hydraulic motor 40is kept braked, and when braking by the turning brake hydraulic motor 40is unnecessary, this is addressed by disconnecting the turning brakehydraulic motor 40 from the turning electric motor 21.

According to the above-described first and second embodiments, byconnecting the turning brake hydraulic motor 40 to the turning electricmotor 21, the turning electric motor 21 is braked, so that theupper-part turning body 3 is braked. Alternatively, the turning brakehydraulic motor 40 may be directly connected to the upper-part turningbody 3 or the turning mechanism 2.

According to the above-described embodiments, a description is given ofthe case where the present invention is applied to a so-called parallelhybrid shovel, where the engine 11 and the motor generator 12 areconnected to the main pump 14, which is a hydraulic pump, and the mainpump is driven. Alternatively, the present invention may also be appliedto a so-called series hybrid shovel, where the motor generator 12 isdriven by the engine 11, electric power generated by the motor generator12 is stored in the electric energy storage system 120, and the mainpump 14 is driven with the stored electric power alone as illustrated inFIG. 7. In this case, the motor generator 12 has a function as agenerator that is driven by the engine 11 to perform a generatoroperation alone. The electric power stored in the electric energystorage system 120 is supplied to an electric motor 400 that drives themain pump 14 through an inverter 18B. When supplied with the electricpower, the electric motor 400 is driven, so that the main pump 14 isdriven.

Furthermore, the present invention may also be applied to an electricshovel, where no engine is provided and a hydraulic pump is driven by anelectric motor alone. FIG. 8 is a block diagram illustrating aconfiguration of a drive system of an electric shovel. The motorgenerator 12 that functions as an electric motor is connected to themain pump 14, and the main pump 14 is driven by the motor generator 12alone. An external power supply 500 is connected to the electric energystorage system 120 through a converter 410. The electric energy storagepart (capacitor 19) of the electric energy storage system 120 issupplied with electric power from the external power supply 500, so thatthe capacitor 19 is charged.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

The present application is based upon and claims the benefit of priorityof Japanese Patent Application No. 2011-076254, filed on Mar. 30, 2011,the entire contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The present invention may be applied to shovels that use an electricmotor to electrically drive a turning body.

DESCRIPTION OF THE REFERENCE NUMERALS

1 lower-part traveling body

1A, 1B hydraulic motor

2 turning mechanism

3 upper-part turning body

4 boom

5 arm

6 bucket

7 boom cylinder

7A hydraulic pipe

7B boom angle sensor

8 arm cylinder

9 bucket cylinder

10 cabin

11 engine

12 electric motor

13 transmission

14 main pump

15 pilot pump

16 high-pressure hydraulic line

17 control valve

18A, 18B, 20 inverter

19 capacitor

21 turning electric motor

22 resolver

23 mechanical brake

24 turning transmission

25 pilot line

26 operation apparatus

26A, 26B lever

26C pedal

26D button switch

27 hydraulic line

28 hydraulic line

29 pressure sensor

30 controller

35 display unit

40 turning brake hydraulic motor

50 hydraulic circuit

50 a, 50 b fluid passage

52A, 52B relief valve

54A, 54B check valve

60 switching valve

70 connecting and disconnecting device

100 step-up/step-down converter

110 DC bus

111 DC bus voltage detecting part

112 capacitor voltage detecting part

113 capacitor electric current detecting part

120 electric energy storage system

400 electric motor

410 converter

500 external power supply

1. A shovel, comprising: a turning electric motor configured to drive aturning body to turn; and a turning brake hydraulic motor mechanicallyconnected to the turning body or the turning electric motor, wherein ina state where a turning operation part for turning the turning body isunoperated, the turning body is braked using the turning brake hydraulicmotor and a braking operation of a mechanical brake unit formechanically holding the turning body stationary is released when anoperation part for performing an operation other than turning of theturning body is operated.
 2. The shovel as claimed in claim 1, furthercomprising: a hydraulic circuit configured to disconnect an intake portand a discharge port of the turning brake hydraulic motor. 3-4.(canceled)
 5. The shovel as claimed in claim 2, wherein the hydrauliccircuit is configured to keep a discharge side of the turning brakehydraulic motor closed, and a connecting and disconnecting device isprovided between the turning body and the turning brake hydraulic motor.6. The shovel as claimed in claim 5, wherein the connecting anddisconnecting device is configured to connect the turning brakehydraulic motor to the turning body or the turning electric motor in thestate where the turning operation part for turning the turning body isunoperated.
 7. The shovel as claimed in claim 2, wherein the hydrauliccircuit includes a switching valve and is configured to disconnect theintake port and the discharge port of the turning brake hydraulic motorby the switching valve.
 8. The shovel as claimed in claim 7, whereinwhen the turning operation part for turning the turning body isoperated, the intake port and the discharge port of the turning brakehydraulic motor are connected by the switching valve to form a closedcircuit, and when the turning operation part for turning the turningbody is unoperated, the intake port and the discharge port of theturning brake hydraulic motor are disconnected by the switching valve.9. A method of controlling a shovel comprising: braking turning body ofthe shovel using a turning brake hydraulic motor mechanically connectedto the turning body or a turning electric motor configured to drive theturning body to turn, and releasing a braking operation of a mechanicalbrake unit for mechanically holding the turning body stationary when anoperation part for performing an operation other than turning of theturning body is operated in a state where a turning operation part forturning the turning body is unoperated.
 10. The method of controlling ashovel as claimed in claim 9, further comprising: disconnecting anintake port and a discharge port of the turning brake hydraulic motorwhen the turning body is braked using the turning brake hydraulic motor.11. The method of controlling a shovel as claimed in claim 10, furthercomprising: keeping a discharge side of the turning brake hydraulicmotor closed, and connecting or disconnecting the turning body and theturning brake hydraulic motor by a connecting and disconnecting device.12. The method of controlling a shovel as claimed in claim 11, furthercomprising: operating the connecting and disconnecting device to connectthe turning brake hydraulic motor to the turning body or the turningelectric motor in the state where the turning operation part for turningthe turning body is unoperated.